1. Field of the Invention
The present invention relates generally to retractable coverings for architectural openings and more particularly to a spool on which a lift cord or other flexible element for such a covering is wrapped.
2. Description of the Relevant Art
Coverings for architectural openings have taken different forms for many years. Early forms of such coverings were simply fabric draped in different manners across an architectural opening such as a window, door, archway, or the like. More sophisticated coverings have involved and include retractable coverings such as roller shades, venetian blinds, collapsible cellular shades and the like. Venetian blinds and some collapsible cellular shades are moved between extended and retracted positions across the architectural opening by a lift cord or other similar flexible element that extends from the headrail downwardly through the covering where it is anchored to a bottom rail. To retract the covering, the lift cord is wrapped around a drum in the headrail by rotating the drum and thereby causing the bottom rail to rise as the lift cord is wrapped about the drum.
As will be appreciated, any time a lift cord is wrapped around a drum, it is prone to becoming entangled in itself and, accordingly, systems have been developed for minimizing entanglement of lift cords about the drums on which they are wrapped. One such system involves shifting the drum linearly as it is being rotated so that the cord is fed sequentially to the drum along the length of the drum surface so that the lift cord is smoothly wrapped around the drum. An example of such a system is disclosed in U.S. Pat. No. 6,129,131 entitled Control System for Coverings for Architectural Openings, which is of common ownership with the present invention.
Some lift cord systems are also designed so that the cord is fed to one end of the drum while it is anchored to the opposite end of the drum creating a catenary in the cord from one end of the drum to the other. These systems work acceptably as long as the catenary is maintained fairly taut. If it is allowed to become slack, the lift cord can easily become undesirably entangled with itself.
It is to provide an improvement over prior art systems for wrapping a lift element about a rotating drum that the present invention has been developed.